Passing tube for vessel for vacuum-degassing molten steel



July 28, 1970 KAMEMATSU MATSUDA ,873

PASSING TUBE FOR VESSEL FOR VACUUM-DEGASStNGMOLTI-IN STEEL Filed April 25, 1967 iNVENTOR.

Kam'emafQu Mafsuda United States Patent Claims Us. (:1. 266-34 5 Claims ABSTRACT OF THE DISCLOS RE A passing tube fitted to the lower part of a molten steel degassing vessel, characterized by that said passing tube is made of a metal case composed of two tubular metals, inside core metal and outside core metal. having an air gap between them, and refractory linings are supported by each core metal and the lower part of the inside lining, the part most likely to be spalled and corroded, which is supported by the outside core metal, may be separately removed from the upper part thereof supported by the inside core metal to make partial replacement possible.

. This invention relates to passing tube provided in the bottom part of a vessel for vacuum-degassing molten steel so that the molten steel may be sucked up from a ladle and discharged into the vessel through the tube.

- An object of the present invention is to make it possible to replace specifically only the remarkably corroded part of a passing tube instead of the entire tube so that the influence of the replacement of the passing tube on the vacuum-degassing vessel may be reduced.

' Another object of the present invention is to prevent the deformation and reduction in strength of core metals of a passing tube by cooling the core metals of the tube likely to be deformed or to be reduced in the strength under the influence of high temperature as their location becoming close to molten steel during the degassing operation.

:A further object of the present invention is to make it possible to use a passing tube to introduce gases into molten steel in a vacuum vessel.

A vacuum refining method, wherein molten steel is degassed while being put into and out of a vacuum vessel, is already known. In such a method the vacuum-degassing treatment is carried out by sucking up molten steel contained in a ladle into a sealed vacuum vessel made of steel and lined with a refractory through a passing tube fitted to the bottom part of said vessel.

For such passing tube has been conventionally used a cylinder made by lining a core metal made of steel with a refractory on the inside and outside. However, the upper part of the passing tube is often heavily damaged 'by being aflected by the high heat of molten steel and by corrosion together with abrasion due to the quick passage of molten steel. The lower part of the passing tube is often damaged by heat impacts as a result of being quickly cooled by being exposed to the atmosphere after the vacuum treatment.

Further, as it is diflicult to use bricks for the structure of the outside lining of the passing tube, the outside lining is usually built by stamping or casting a plastic refractory powder. However, such part is also heated and cooled so quickly that it is required to be high in the antispalling property. But, the refractory high in the antispalling property has a defect that it is weak against the corrosion by slag present on molten steel contained in the 3,521,873 Patented July 28, 1970 ladle or against the mechanical stress when removing slag.

Any refractory which will perfectly meet such requirements as are mentioned above for inside and outside linings of a passing tube or a method of applying it has not yet been discovered. For such reasons, a cylindrical passing tube for a vacuum-degassing vessel has been re movably fitted to the lower part of the vacuum vessel so that, in case the lining has been remarkably damaged, the tube may be removed from the flanged part and may be replaced with a separately prepared passing tube. However, if the replacement of the passing tube is carried out frequently, the lining in the lower part of the vacuumdegassing vessel, to which the passing tube is fittted, is locally damaged as a result of being exposed to the outside atmosphere and cooled down, whereby the life of the vessel is largely reduced. Therefore, it is necessary to decrease the frequency of the replacement of the passing tube to be as low as possible.

The present invention has it for an object to reduce the influence of the replacement of the passing tube on the vacuum-degassing vessel by making replaceable only the remarkably corroded part of the passing tube instead of the entire tube. Another object of the present invention is to make the passing tube applicable to introduce gases into the molten steel contained in the vacuum vessel.

Thus, according to the present invention, a passing tube to be provided in the lower part of a vacuum-degassing vessel is formed of double inside and outside core metals (tubular metals), a clearance is provided between said inside core metal and outside core metal, the inside core metal is secured to a flange jointed with the bottom part of the vacuum-degassing vessel, the outside core metal is fixed to a flange provided on said inside core metal, a refractory lining is supported by each core metal, the lower part of the inside lining of the passing tube, which part is most likely to be spalled, is made separable from the lining in the upper part and further, if required, said lower lining is formed of porous gas-permeable bricks.

The subject matter of the present invention shall be explained in the following with reference to the drawing.

Figure is a sectioned view illustrating the structure of a passing tube of the present invention.

In the drawing, 1 is an inside core metal supported by a flange 2 jointed with the bottom part of a vacuumdegassing vessel and upper and lower linings of different materials are fixed to said core metal. That is to say, the upper lining 3 is built of anticorrosive and wearresistant firebricks through a castable material 11 and is supported by a flange 12 projected on the inside core metal 1. The lower lining 4 is made of bricks high in the antispalling property and is supported by a flange 13 on an outside core metal 5 or, as required, by the inside core metal 1. On the other hand, a lining 10 of a refractory is applied also to the outside of the outside core metal 5 provided through an air gap 7 outside the inside core metal 1. Therefore, the top parts of the firebricks of the inside lining 3 are in close contact with bricks in a throat part in the opening part in the lower part of the vacuum-degassing vessel and the lower ends of said firebricks are in contact with the upper end of the lower lining 4. Further, a flange 6 is provided on the outside core metal 5. This flange 6 is air-tightly jointed through bolts or the like (not illustrated) with a flange 6' secured to the inside core metal 1.

The air gap 7 is provided as described above between the inside core metal 1 and outside core metal 5 so that it may not be made difficult by the deformation at the time of the use to engage or disengage the two core metals with each other. Therefore, by removing the bolts joint- 3 ing the flanges 6 and 6 in close contact with each other, the lower lining 4 of the passing tube fitted to the outside core metal 5 and the outside refractory lining can be easily removed for replacement together with the outside core metal 5 from the vacuum-degassing vessel and the upper part of the passing tube jointed with it, that is, from the upper lining built in the inside core metal 1.

Therefore, if the entire tube may be replaced by repeating several times the partial replacement, in which only the inside lower lining 4, which. is easily damaged by the operation of vacuum-degassing of molten steel because of lacking in the anticorrosion, though having an antispalling property, and the outside lining 10, which is also easily damaged by high temperature, are replaced, the operation can be carried out very economically and the influence on the vacuum-degassing vessel is largely reduced.

Further, according to the present invention the protection of the inside core metal 1 can be secured, which is easily overheated and consequently deformed and reduced in the strength, because it comes nearer to molten steel during the vacuum-degassing operation. That is to say, the inside core metal 1 is the place, where the deformation due to creeps or the reduction in the strength due to oxidation easily occurs, as being under the influence of high temperature of molten steel. However, according to the present invention, the said difficulty can easily be eliminated, as the core metal 1 can be cooled down by means of cold wind blown at a high speed into the air gap 7 provided between the inside and outside core metals through an inlet pipe 8, which is communicated with said air gap, and discharged through an outlet pipe 9.

Further, the passing tube of the structure of the present invention can be utilized also to introduce inert or other gases into the vacuum vessel to elevate the effect of degassing the molten steel. That is, the lining 4 fitted to the outside core metal 5 in the lower part of the passing tube may be formed of porous gas-permeable bricks or perforated bricks so that, when gases are blown into the air gap 7, said gases may be introduced into the molten steel through the lining 4 of the porous gaspermeable bricks or perforated bricks. The introduced gases will act to cool the inside core metal 1 and, on the other hand, will be preheated before being introduced into the molten steel. Further, it is to note that when such a gas-permeable refractory of porous structure is used for introducing gases, it has usually no resistance to the quick flow of molten steel and is likely to corrode. In such a case the construction of the present invention has an advantage that the partial replacement is feasible, because the inside lining is divided into upper and lower parts, as above mentioned.

Thus, in the present invention, as only the heavily damaged part of the lining of the passing tube can be partly and freely replaced, not only the life of the passing tube can be elongated, but also the influence of the replacement of the passing tube on the bottom part of the degassing vessel can be largely reduced.

Having thus described the invention, what is claimed 1. A passing tube assembly for degassing molten steel, said tube attachable to the lower part of a degassing ves- 4 sel for molten steel to suck and discharge the molten steel as from a ladle therebeneath, said tube assembly comprising in combination:

(a) a metal core generally constituting the passing tube and composed of double, inside (1) and outside (5) tubular core metals spaced peripherally apart for air gap clearance therebetween when assembled with the latter around the former;

(b) said inside core metal (1) attached generally at one end, constituting an upper end when said tube is vertically disposed, to a flange (2) having an open center and attachable to the bottom part of a vacuum-degassing vessel for communication with the molten steel therein;

(c) said inside (1) and outside (5) core metals each having a radial projecting flange (6') and (6) attached generally transversely to their outer peripheral surface near the upper ends thereof, and including complemental adjoining faces with means for interconnecting same in a sealed, air tight manner to help define said clearance space in an air tight sealed manner between said core metals;

(d) a lining for said tube including a co-extensive inside lining having a separable lower portion (4) and an outside lining (10) supported, in a generally concentric manner relative to one another, by means on said outside core metal (5) so that said outside lining and said lower portion (4) of the inside lining together may be removable by disassembly of said outside core metal (5) from around said inside core metal (1).

2. The passing tube according to claim 1 including means for introducing gases between said inside core metal (1) and said outside core metal (5) so that the inside core metal may be cooled.

3. The passing tube for degassing molten steel according to claim 1 wherein said lower inside lining supported by said outside core metal (5) is formed of porous gaspermeable bricks so that gases blown into the air gap provided between the inside core metal (1) and the outside core metal (5) may be introduced into the molten steel through said bricks.

4. The passing tube for degassing molten steel claimed in claim 3, wherein the lower inside lining supported by the outside core metal is formed of perforated bricks.

5. The passing tube for degassing molten steel according to claim 2 wherein said lower inside lining supported by said outside core metal (5) is formed of porous gaspermeable bricks so that gases blown into the air gap provided between the inside core metal (1) and the outside core metal (5) maybe introduced into the molten steel through said bricks.

References Cited UNITED STATES PATENTS 2,906,521 9/1959 Harders. 3,131,243 4/1964 Lorenz. 3,353,809 11/1967 Snellman. 3,380,727 4/ 1968 Ruttiger et al.

J. SPENCER OVERHOLSER, Primary Examiner J. E. ROETHEL, Assistant Examiner 

